This core will generate mouse models carrying null (knockout) and knock-in mutations. By generating such models we will be able to a) model human disease phenotypes and determine the consequences of mutations on organ development, b) assay for alternative functions of developmental genes which may underlie pleiotropic expression in humans, c) identify and/or confirm downstream targets and upstream regulators of gene function, d) target mouse genes as a way of identifying cognate human osteochondrodysplasias. The core facility will provide animal sfor each of the four research projects in this Program Project.